The content of macroelements Ca, K, Mg and N, as well as of trace elements Fe, Mn, Cu, Zn and Pb has been studied in different phytomass fractions (leaves, bark, annual and perennial branches, catkins, cupolas, acorns, litter and mulch) and in soil horizons in three sweet chestnut communities – various in age and management activities in Belasitza mountain. The coefficient of biological absorption is calculated for all fractions and elements, and the elements turnover intensity is determined. Disturbances in studied functional parameters were determined, which is also connected with the observed health status of sweet chestnut forests in the mountain.
Key words: sweet chestnut forests, Belasitza mountain, macroelements, trace elements
According to data collected from European countries, sweet chestnut forests in Europe cover 2 000 000 ha, and 80% of them are private (Amorini et al., 2000). On the Balkan Peninsula, the occurrence of sweet chestnut communities is in direct dependence from Mediterranean and Black Sea climatic influence (Le Houerou, 1992). In Bulgaria, the sweet chestnut areas cover 3356 ha (data from 2003), which is only 0.1% of the forest fund. In spite of the various hypotheses about the provenance of sweet chestnut in Bulgaria, it is considered for the present that only 500 ha of the forests are natural (Kochev, 1973; Dobrinov et al., 1992). The degradation of sweet chestnut forests in Europe is considered to be a serious problem in the end of the 1970s. The main hypothesis for their poor condition, together with the global climatic changes and land use problems, is the predomination of ageing
stands. Castanea sativaMill. ecosystems have been an object of study within the projects ‘Sustainability of Mediterranean ecosystems – case study of the chestnut forest, 1994-1997’ and ‘Multidisciplinary chestnut research – COST Action G4, 1998’ (Romane, Grossman, 1997b; Heiniger et al., 2001). Even today the hard work for improvement of sweet chestnut forests continues in Western Europe. The most serious threats for sweet chestnut communities today are in disease (Phytophthora species), bark cancer (Cryphonectria parasiticaMurr. (Syn. Endothia para-siticaMurr) and the spreading of Loranthus europeusL. (Bourbos, Metzidakis, 2000; Vannini, Vettraino, 2001; Heiniger et al., 2001; Petkov, Rossnev, 2001). Sweet chestnut is also attacked by other diseases and pests on bark, leaves and acorns. For example, fungi from genus Melancolis, the dangerous chestnut weevil (Curculio elephasGyll.), etc. The spreading of diseases and pests depends on environmental, biotic (community and hu-man) factors – utilisation and management. During the last years, increasing interest is observed on the side of the society towards sweet chestnut, due to quality of timber, delicious acorns (with utilisation in food, pharmaceutical and cosmetics industries) and to the fact that communities are suitable for multifunctional management (Kitanov, 1986; Amorini et al., 2000; Bra-tanova-Doncheva et al., 2002).Basic directions, on which it is being worked to reduce degradation processes, are: determination of ecosystem criteria (structure and functions of sweet chestnut com-munities) and biological criteria (creation of sustainable sorts through improvement and hybridization with Castanea crenataSieb. et Zucc. and Castanea mollissimaBl.) for sustainability of communities, development of models for silvicultural intervention and way of utilisation and of pest control models. Numerous works have been published, concerning spreading, biology and phy-tocoenology of the species, its ecological requirements, diseases and pests, ideas about establishment of sweet chestnut plantations, improvement, introduction and hybridisa-tion of sustainable sorts (Zhelyazkov et al., 1980; 1982; Bratanova-Doncheva et al., 1995;
1998а,b; 2002; 2003; Marcelino et al., 2000; Queijeiro et al., 2000; Velev et al., 2000). The dynamics of sweet chestnut ecosystems is very fast and, in absence of man-agement, they turn into mixed deciduous forests, which is due to the invasion of shade tolerant broadleaved species (Conedera et al., 1998). Similar processes are observed in Western Balkan range – gradual replacement of sweet chestnut forests with Fagus sylatica L. and Carpinus betulusL. ones (Kochev, 1973; Lyubenova et al., 2002a,b; Bratanova-Doncheva et al., 2002). In Bulgaria, sites of Castanea sativaMill. are under special protection in the list of types of natural habitats of EU interest, which protection requires determination of ‘zones under special protection’ (type 9260 – Sweet chestnut forests) of Directive 92/43/ЕЕС (Council Directives 92/43/EEC; Bratanova-Doncheva, 2003). According to the degree of threat, sweet chestnut refers to the category ‘species threatened of extinction’. The assessment of ecosystem criteria for sustainability of sweet chestnut forests re-quires profound complex studies on the structure and functioning of communities. For example, studies on biogeochemical turnovers have been carried out in Portugal by Pires et al., in Spain by Gallardo-Lancho et al. and Santa Regina et al., in Italy by Leonardi et al. and in France by Romane et al. (1997a,b). The aim of this research is to make a comparative analyses of macro- and micro-element content and some geochemical coefficients in different phytomass fractions and investigated communities.
The present investigation is part of a complex study on structural and functional parameters of sweet chestnut communities in Southwest Bulgaria and has the aim to lay the application of ecological management of sweet hestnut forests in Bulgaria on scientific fundaments.
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